This invention relates to a coupling capable of easily connecting a corrugated pipe which is often used as a pipe for supplying domestic gas or the like.
Japanese Laid-Open Utility Model Application No. Hei 3-52493 discloses a coupling capable of easily connecting a corrugated pipe through simple insertion. Specifically, a body of this coupling has a through-hole whose one end is served as an inlet port. A first and a second annular accommodation recesses are formed, in this order, in the through-hole in a manner axially spacedly away from the inlet port. An engagement member, which is formed of a coil spring whose both ends are connected together so that the coil spring forms an annular shape, is accommodated in the first accommodation recess, while an annular seal member is accommodated in the second accommodation recess. The first accommodation recess is defined by two side surfaces. One of the two side surfaces nearer to the inlet port is tapered and the other is disposed perpendicular to the axis. The engagement member and seal member are mounted to the body before the corrugated pipe is connected. When a distal end of the corrugated pipe is inserted from the inlet port of the body, all turns of the engagement member are deformed to an elliptical shape from a circular shape each time the ridges of the corrugated pipe pass the engagement member, and restored to the original circular shape each time the grooves pass the engagement member. The corrugated pipe advances further into the body through repetition of the foregoing procedure several times, and the distal end of the corrugated pipe is inserted into the seal member. When the distal end of the corrugated pipe comes into contact with a step formed in the body, the corrugated pipe is prohibited from further advancing. In this way, the corrugated pipe is connected to the coupling. In that state, by intimately attaching the seal member to an outer periphery of the corrugated pipe such that the seal member is elastically deformed, the corrugated pipe and the body are sealed. When a withdrawing force is applied to the corrugated pipe, a radial outward force is applied to the engagement member from a tapered surface of the corrugated pipe. However, since a radially inward force (that is, force for pushing the engagement member back to the grooves of the corrugated pipe) is applied to the engagement member from the tapered surface of the first accommodation recess, the engagement member is deformed to an elliptical shape, thus being prohibited from climbing over the ridges of the corrugated pipe.
However, the coupling of the above Publication No. Hei 3-52493 has the following inconveniences. That is, since the engagement member is merely accommodated in the first accommodation recess, when a comparatively small amount of shock is applied to the coupling, in which the engagement member is already received in the body in a factory, during its transportation to a working site, the engagement member is dropped from the coupling. Moreover, since the engagement member climbs over the ridges of the corrugated pipe due to elastic deformation of each turn when the corrugated pipe is inserted into the coupling, the engagement member receives a force directing toward the grooves from the inner peripheral surface of the first accommodation portion. The result is that insertion resistance is increased.
In couplings illustrated in FIGS. 3 and 4 and also in FIGS. 5 and 6 of Japanese Laid-Open Utility Model Application No. Hei 3-91592, the through-hole of the body has an annular accommodation recess whose inner peripheral surface is tapered. A seal member having a tapered outer peripheral surface and an annular engagement member are beforehand received in this accommodation recess. The engagement member is formed in an annular shape by connecting both ends of a coil spring with each other. The engagement member is secured to an end of the seal member when the latter is molded. The seal member is biased toward an inlet port of the through-hole by another coil spring. In the coupling thus constructed, when a corrugated pipe is inserted into the through-hole of the body, a ridge of the foremost end of the corrugated pipe contacts the engagement member to move the engagement member further into the accommodation recess together with the seal portion. The seal member is limited its movement when it contacts an inner end of the accommodation recess. When the corrugated pipe is further advanced, the distal end of the corrugated pipe is inserted into the seal member passing through the engagement member. The engagement member is elastically enlarged in diameter each time the ridges of the corrugated pipe pass. After the ridges have passed, the engagement member is reduced in diameter and engaged in the grooves. Thereafter, when the worker releases his hold of the corrugated pipe, the seal member, the engagement member and the corrugated pipe are moved in the opposite direction to the inserting direction and the tapered outer peripheral surface of the seal member contacts the tapered inner peripheral surface of the accommodation recess, thereby sealing the body and the corrugated pipe. The engagement member, while being engaged in the grooves of the corrugated pipe, contacts a tapered retainer surface formed at the inlet port of the through-hole, thereby preventing the corrugated pipe from coming off.
However, in the coupling of the above Publication No. Hei 3-91592, nevertheless there is a change in insertion resistance each time the engagement member climbs over the ridges of the corrugated pipe a plurality of times, the worker cannot clearly recognize the completion of the connection work of the corrugated pipe to the coupling.